1. Field of the Invention
The invention relates to a brake pad with a backing plate, a friction material layer and a wear indicator.
2. Description of the Related Art
All modern ground transportation, that is motorcycles, bicycles, automobiles, trucks, construction equipment and even airplanes during taxi, takeoff and landing, control deceleration by converting the vehicle's kinetic energy or mass velocity, into heat by a system of friction braking.
Generally a pad and a rotor or a shoe and a drum configuration are used. The pad or shoe (made of a special friction absorbing material) is connected to the vehicle, and is pressed against a metal rotor or drum attached to the rotating axle or wheel. As the friction part is pressed against the rotating part, energy is absorbed, and the vehicle decelerates.
The friction material is constructed to maximize strength, friction co-efficient and heat tolerance, but not be so hard, hot, or abrasive as to wear away at the more-expensive rotating metal rotor or drum.
The ablative friction material is sacrificial, as it is intended to be ablated or slowly used up during repeated braking applications. It is in the process of using up the friction material that braking is disturbed and catastrophic danger and damage occur. Wear-through of the brake pads can create an emergent brake failure and the resultant metal-to-metal contact can erode expensive parts.
It therefore becomes crucial for the vehicle operator to have a reliable indication of the impending wear-through. A simple, reliable, failsafe, clearly visible, low maintenance, all wheel, direct measuring contrasting color brake wear indicator would be an advancement to the art.
According to the March, 2004 issue of Consumer Reports, there are four general types of brake pads for cars and trucks. Semi-metallic pads contain metal or graphite mixed with inorganic fillers and friction modifiers for bonding. Non-asbestos organic pads have a mixture of non-asbestos fibers with filler materials and high-temperature resins.
Low-metallic NAO pads are made from an organic formula mixed with metal for heat transfer and braking. Ceramic pads have ceramic fibers, non-ferrous filler materials, bonding agents and possibly small amounts of metal. These types of pads differ in durability, heat transfer, wear, noise, dust emission and their effect on other parts of the system, such as rotors.
Thus, normal brake pad or shoe material may be a strong matrix of tough aramid fibers, rock hard, sharp edged, friction particles and heat resistant hardening resin. Brake pads suffer extremes in mechanical forces and temperatures. Their integrity depends on a uniform cohesiveness throughout the pad or shoe and an equal adhesive quality in attachment to the backing plate.
Direct measuring brake wear indicators are grooves or rivet holes cut in the pads or shoes that require partial or complete disassembly of the braking system to indicate wear level. The special equipment, expertise, and expense involved, have effectively negated the indicators having grooves or rivet holes.
Thin metal noise makers (blades or springs mounted on the pads) are only mounted on front brakes and have limited use because they are not used on rear wheels, trailers, buses, large trucks, construction equipment or airplanes. They must also be heard above the operating noise of the vehicle and their horns, radios or music system.
Indirect measuring brake wear indicators do not measure the remaining brake thickness but measure only the distance between the metal braking plate and the metal rotor or drum. They not only suffer that inaccuracy, but lack reliability and increased maintenance, inherent to their complexities of gears, cams, followers, pins, contacts, electric wires, circuit breakers and lights. They are especially failure prone in the hostile environment of the exposed wheel location, with high “G” loads, vibrations of the bouncing wheels and exposure to dirt, water, ice and road salt.
None of the prior art provides a self-test or failure warning. Wear through, brake failure and extreme repair costs are still common.
Another prior art device provides a color layer brake wear indicator. The pad or shoe is made in layers of contrasting colors. The major working thickness of the pad is standard ablative friction material that sheds the typical dark brake dust. The bottom reserve or danger zone of the pad is made of a brightly colored material that functions as an indicator by shedding a colored brake dust, which is visible on the wheel and rims. This shedding of colored material is easily visible to the operator as the vehicle is approached, fueled or cleaned. Dark dust equals normal wear and colored dust gives a clear indication of brake wear. Such a device is known from Comp Mountain dual color pads manufactured by Jagwire for mountain bikes. The prior art homogeneous colored layer is not failsafe but instead is failure prone. Two dangerous structural faults are present.
The homogeneous colored layer of soft material displaces the stronger material and a cohesive fault zone of weakness is created. Colored particles are smooth, soft and weak and the adhesiveness to the backing plate is minimal. The tremendous shear forces of braking are inline with this soft fault line, so that pad separation results and total brake failure occurs.
The homogeneous layering of soft, smooth non-friction particles also causes a sudden loss of brake efficiency once the colored layer is uncovered. The colored particles instantly coat the exposed layer with an ineffective surface of minimal friction. This soft substance acts as a lubricant, as braking friction suddenly drops and brake failure occurs.
A homogeneous colored layer used as a brake wear indicator is flawed and unacceptable.